THE PLURISERIAL RIBEIRA MAGMATIC SYSTEM 590, SE / S BRAZIL AND URUGUAY

EBERHARD WERNICK

Resumo


The Pluriserial Ribeira Magmatic System-590 (PRMS-590) which acted in the Late Precambrian Ribeira Belt in SE/S Brazil, and Uruguay about 580 - 610 Ma ago, is described and discussed. The system, developed during the Post-Collisional Mentation & Uplift evolutional stage of the Ribeira Belt, comprises mainly six groups (series) of high-K rocks: (1) alkali-calcic Caledonian I-type metaluminous (quartz) monzonites & syenites and monzo-, syeno- & alkali-feldspar granites; (2) alkali-calcic metaluminous (quartz) monzonites & syenites and monzo-, syeno- & alkali-feldspar rapakivi granites; (3) shoshonitic metaluminous ± fayalite ± pyroxene ± hornblende ± biotite (quartz) monzonites & syenites and monzo-, syeno-& alkali-feldspar granites sometimes with rare late crystallised mafic soda minerals; (4) peralkaline mafic soda minerals bearing (quartz) monzonites & syenites and monzo-, syeno- & alkali-feldspar granites with or without ± fayalite ± pyroxene ± hornblende ± biotite; (5) K-alkaline metaluminous suites of ± (quartz) gabbros & monzogabbros ± (quartz) monzodiorites & diorites ± (quartz) monzonites & syenites and granites and (6) ultrapotassic under- and oversaturated monzonites & syenites with variable amounts of orthopyroxene. These rocks are either of lower crustal (1,2, and possibly 3) or mantelic origin (4, 5, 6), a fact which indicates the simultaneous melting of lower crust and secondary enriched mantle during that time. Several tectonic, geochemical and isotopic aspects are presented to show the internal coherence of the PRMS-590.

Palavras-chave


Ribeira Fold Belt; Brasiliano Cycle (Late Precambrian); Magmatic System; SE/S Brazil; and Uruguay; High-K rocks.

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